1. Field of the Invention
The present invention relates to a mechanism for cutting a sheet of paper that is discharged from a roll incorporated in a facsimile or copying or printing machine into a desired size. More particularly, the present invention relates to a sheet cutting mechanism of the type that moving a blade holding carriage along a straight rail extending across a sheet causes the blade to cut the sheet into a desired length or size.
2. Description of the Related Art
JP-A 6-134692 discloses a sheet cutting mechanism that includes an elongate straight blade, which is hereinafter called as a stationary blade, and a displaceable blade. In the known mechanism, cutting a sheet of paper is conducted by, with the displaceable blade held against the stationary blade, moving the displaceable blade along the stationary blade. This is further described in connection with FIG. 14.
Referring to FIG. 14, the stationary blade is designated by the reference numeral 20. The stationary blade 20 is fixedly attached to a cutter frame 21 on a downwardly facing surface such that the stationary blade 20 extends in the longitudinal direction of the frame 21. The frame 21 is bent, at its one edge portion, upwardly to define a guide 22 for motion of a carriage. The stationary blade 20 extends along the guide 22.
The carriage 23 includes a holder 24 that is recessed to receive the guide 22. An arm for unitary motion interconnects the carriage 23 and a rotary blade support 25. Thus, the rotary blade support 25 is permitted for reciprocal motion along the guide 22 in the longitudinal direction of the stationary blade 20. Two pulleys are arranged at portions adjacent the remotest, in the longitudinal direction, ends of the stationary blade 20. One pulley out of them, which is disposed on this side viewing in FIG. 14, is mounted to receive torque from a motor via a drive shaft, a pinion on the drive shaft and an appropriate gearing. A wire is wound around both of the pulleys and tensioned between the pulleys by, for example, a coil spring. The wire engages, at its appropriate portion, the carriage 23. Torque of the motor is transmitted through the pinion, gearing, pulley and wire to the carriage 23, urging the carriage 23 for reciprocal motion along the guide 22. At its outer periphery, the carriage 23 has a leading paper guide portion 27 and an escape groove 28. As the carriage 23 advances along the guide 22, the paper guide portion 27 guides paper toward a contact point between the stationary and rotary blades 20 and 26 (this contact point being hereinafter called as a cutting point). During the movement of the carriage 23, the escape groove 28 permits evacuation of the portion of paper, which has been cut.
The arm interconnects the carriage 23 and the rotary blade support 25 for unitary motion. The rotary blade 26 and stationary blade 20 overlap each other at their edge portions. The rotary blade 26 is urged into press-contact with the stationary blade 20. Although not illustrated in FIG. 14, the rotary blade 26 has, on its hidden surface, a pressure disc (a turning wheel) connected thereto for unitary rotation therewith. As a portion of this pressure disc is always held in contact with the stationary blade 20, movement of the carriage 23 causes the rotary blade 26 to turn and move along the edge of the stationary blade 20.
It is now described how the sheet cutting mechanism operates to cut the sheet of paper from a roll. The carriage 23 waits for a call at one position, namely standby position, which limits movement of the carriage 23 in FIG. 14. When the motor pulls the wire, the carriage 23 moves along the guide 22, causing the rotary blade 26 that is carried by the rotary blade support 25 to move along the stationary blade 20. The rotary blade 26 is held in press-contact with the stationary blade 20 during this movement. The rotary blade 26 is urged to turn during this movement owing to the pressure disc pressed against the stationary blade 20. Upon or immediately after the carriage 23 having reached the beginning end of the paper, the leading guide portion 27 on the front end of the carriage 23 starts guiding the paper toward the cutting point. The rotary blade 26 and the stationary blade 20 cooperate with each other to cut the paper at the cutting point The portion of the paper that has been cut is evacuated away from the cutting point by the escape groove 28 so as not to interfere with the cutting operation. When the carriage 23 has reached the opposite limit position after completion of cutting operation of paper, the motor is reversed, pulling, via the wire, the carriage 23 in the opposite direction, and returning the carriage 23 to the standby position. One cycle of cutting operation ends when the carriage 23 has returned to the standby position.
An improved version of the sheet cutting mechanism of the kind described above is proposed in JP-A 7-124892. FIG. 15 shows one embodiment of a sheet cutting mechanism incorporating this proposal. According to this proposed sheet cutting mechanism, a rotary blade 26 is angled with respect to a stationary blade 20 such that the edge of the rotary blade 26 engages the edge of the stationary blade 20 at a single contact point. During movement of a carriage 23 for cutting operation, the rotary blade 26 is urged to turn owing to moment occurring at the contact point.
There have been proposed sheet cutting mechanisms that do not employ a stationary blade. JP-A 7-100791 and JP-A 7-24782 disclose inventions relating to the sheet cutting mechanisms of this type.
FIG. 16 shows a fragmentary perspective view of a sheet cutting mechanism proposed by JP-A 7-100791. In this known cutting mechanism, a rotary blade 30 and an auxiliary blade 31 are mounted in a holder 32. The rotary blade 30 rotates and cooperates with the auxiliary blade 31 to cut the sheet in response to movement of the holder 32.
JP-A 7-24782 proposes transversely cutting a sheet of paper with a pair of circular blades; each carried by portions of a holder. The holder portions are interconnected by a coupling portion that is disposed in the trailing side of the circular blades with respect to movement of circular blades for cutting operation. During movement of the holder to cross the sheet of paper, the circular blades are urged to rotate to pull the paper toward a cutting point at which the circular blades engage each other.
FIG. 17 is a fragmentary perspective view of the sheet cutting mechanism disclosed in JP-A 7-24782.
Referring to FIG. 17, in this cutting mechanism, the holder 40 has pivoted thereto two circular blades 41 and 42. The circular blades 41 and 42 are disposed on one and the opposite sides of sheet of paper to be cut. The circular blade 41 is slightly angled with respect to the circular blade 42. This arrangement permits the circular blades 41 and 42 to engage each other at a single contact point to form one intersection, which contributes to cutting of paper, of two intersections of the outer peripheries of the circular blades 41 and 42. At least one of the two circular blades is urged to turn in response to movement of the holder 40. The holder 40 includes the coupling portion 44, which interconnects the holder portions, each supporting one of the circular blades 41 and 42, in order to allow a single rail to guide the holder 40. The coupling portion 44 is disposed in the trailing side of the two circular blades 41 and 42. In order to guide paper discharged by the circular blades 41 and 42 away from the coupling portion 44, the holder 40 is provided with a guide portion 43.
In the sheet cutting mechanisms, the blades move at high speeds. Thus, the performance of the cutting mechanisms depends heavily on how easily the blades can cut into the paper initially. If it is required to cut the paper easily and quickly, what one has to do is to make an initial cut into the paper from its edge and then, with the scissors held open, press the scissors in a direction you desire. This belongs to the common knowledge in every day life. If the paper to be cut is of the wet type, such as heat-sensible paper used in facsimile or printing machines, so-called "press cutting" technique is not recommendable. In this case, it is recommended to pivot the blades of the scissors to cut the paper.
The known sheet cutting mechanisms discussed above show good cutting quality, but fail to show any measure to accomplish a smooth cut-in. Further discussion is made in connection with FIGS. 12(a), 12(b) and 12(c). FIG. 12(a) shows, in arrows, a load which the paper is subject to upon making an initial cut by the known sheet cutting mechanism using the circular blade 26 in combination with the stationary blade 20. FIG. 12(b) shows, in arrows, a load, which the paper is subject to upon making an initial cut by the sheet cutting mechanism using the circular blade 30 in combination with the auxiliary blade 31. FIG. 12(c) shows, in arrow, load, which the paper is subject to upon making an initial cut by the sheet cutting mechanism using the two circular blades 41 and 42. As seen from FIGS. 12(a), 12(b) and 12(c), the paper is pressed owing to reaction upon making an initial cut. This hampers smooth operation to make an initial cut into the paper. This problem will be solved if the edge of paper is pressed on a stand or circular blades extremely large, in diameter, are used. However, these measures induce other problem that the setting quality of paper become worse or the number of component parts increases excessively or the cutting mechanism becomes bulky. Thus, one must expect some load to which the paper is subject to, and slanted or notched surface resulting from cutting the paper inwardly as deep as 10 mm. In high humidity, the paper of the wet type, such as thermograph paper, tends to jam. Particularly, in the sheet cutting mechanism described in JP-A 7-100791 or JP-A 7-24782, the paper cutting surface is separated from the edge of the stand, on which the paper is set, so that the paper is subject directly to the influence of the force tending to press the paper. In these cutting mechanisms, the circular blade is improved in its cutting quality and/or it is well arranged, enhancing the cutting quality of the cutting mechanism for its increased cut-in capability, thus reducing the influence of the force tending to press the paper.
There is another task to be accomplished.
In the sheet cutting mechanism using the stationary blade and the circular blade, the stationary blade is very expensive. This is because, in order to provide good cutting quality, the stationary blade must be straight and flat to a preset high degree of precision, and steel must be used as the material of the stationary blade. JP-A 7-124892 teaches the use of a product resulting from punching out a stainless steel belt as the stationary blade. However, further cost reduction cannot be expected because the material itself is expensive.
The sheet cutting mechanisms described in JP-A 7-100791 and JP-A 7-24782 do not use a stationary blade and thus they are advantageous upon reduction of cost. In the case of the sheet cutting mechanism of JP-A 7-100791, the circular blade and the auxiliary blade, which are displaceable with the carriage, engage each other at contact points that are unaltered. In other words, the auxiliary blade is subject to local stress at the contact points whenever the carriage moves, causing excessively quick deterioration of the cutting performance. JP-A 7-100791 teaches the use of a circular rotary blade as the auxiliary blade. However, there is no description as to the structure of such circular rotary blade. Thus, it appears that this teaching does not involve anything beyond what is described in JP-A 7-24782 with regard to the sheet cutting mechanism.
The sheet cutting mechanism according to JP-A 7-24782 is further described in connection with FIG. 13(c). FIG. 13(c) shows an opening angle of the sheet cutting mechanism using two circular blades. In the sheet cutting mechanism of JP-A 7-24782, the two thin disk-like circular blades engage each other at a single point. In this case, as shown in FIG. 13(c), the opening angle defined between the two circular blades becomes inevitably large. This state may be referred to as scissors with its blades opened widely. Thus, the cutting quality is not good. It is well known as the everyday common sense that scissors provide good cutting quality upon pressing through the paper if its blades are held opened less widely. In order to improve the cutting quality, what is needed is to increase force with which the two circular blades engage each other at a single contact point where the sharp-edged circular blades meet. In this case, it is likely that the edges are damaged. In this known mechanism, one of the two circular blades is urged to rotate and the other follows this rotation during cutting operation. Satisfactory cutting performance cannot be expected, however, because the rotation of the other circular blade tends to be unstable. In this conventional cutting mechanism, the circular blades engage each other in overlapping manner so that they overlap the paper during cutting operation. With this arrangement, the other circular blade contacts the remaining portion of the paper during cutting operation, posing problem that the circular blade might scratch the paper. This causes the paper to flutter, inducing occurrence of "jamming".
Thus, it is difficult to apply the conventional sheet cutting mechanism that uses the circular blade in cooperation with another circular blade or auxiliary blade to apparatuses, for example, facsimile, printer or the like, that use thermograph paper. These apparatuses have used the cutting mechanism that uses the circular blade in cooperation with the stationary blade or the cutting mechanism of the so-called guillotine type. One representative example of the guillotine type cutting mechanism is disclosed in JP-B 50-24466.
An object of the present invention is to provide a high performance inexpensive sheet cutting mechanism that has combined the merits of the conventional cutting mechanism that uses the circular blade with the stationary blade with the merits of the conventional cutting mechanism that uses the two circular blades.